The present invention relates to novel compositions and methods that are of use in the verification of products or documents. The compositions and methods are based on the reading of emitted light from luminescent compositions that can be incorporated or applied to a wide variety of materials.
Accurate verification of products and documents is critical to a wide variety of industries including the manufacture of pharmaceutical, clothing, automotive parts, and the issuance of credit and identification cards or travel/immigration documentation. Counterfeiters of products, currency and documents have developed increasingly sophisticated methods of detecting and copying of marks and labels.
Counterfeiting and product diversion cost owners of products, brand names, and intellectual property billions of dollars annually on a world-wide basis, according to the International Anti-Counterfeiting Council (IACC). The problem in the United States, for example, encompasses an estimated loss in revenues of $200 billion per year, as well as associated costs in tax revenues and the loss of jobs.
Current technologies being used to address this problem are varied. The use of chelates as security markings is described in U.S. Pat. No. 5,837,042 to Lent et al. However, the patent is limited because it fails to describe any chelate ligands beyond the class of 1,3-diketones or salicylic acid. Also, the patent only uses the chelates in ink jet printing applications. Therefore, this invention is limited to very specific applications. Also, the 1,3-diketone ligands do not show long term stability to light. In common use, this is an important consideration, because labeled or marked goods or documents are subjected to changes in temperature, humidity, exposure to light, and other environmental perturbations.
Accordingly, there is a continuing need to develop new compositions and methods for product verification and security identification of goods and documents in common use.
As a solution to the above-related deficiencies in the prior art, the present invention is directed to comparing luminescent markings of novel chelates for a variety of substrates, such as paper (e.g. currency, stocks, bonds), cloth (or threads), plastic (e.g. plastic cards), leather, metal, glass, or other convenient forms may be used. These markings provide a code that is read as an image, a wavelength (color), and a luminescent decay time. The new chelates show superior absorption and energy transfer features, particularly for sensitizing the luminescence of europium and terbium metals. In addition, the new chelates have a high stability toward photochemical decomposition rate. Moreover, a class of luminescence lifetime modifiers (e.g. derivatives of imidazole that serve as ancillary coordinating ligands), is used in conjunction with a variety of chelates in order to produce a matrix of variables that include emission wavelength and decay time. It is further contemplated that a combination of one or more compositions having variable lifetimes can be scanned for recording wavelength and decay time with high fidelity. Also described is a simple inexpensive detector that is used for the collection and communication of luminescence data.
The present invention contemplates light-based technology that introduces varied levels of discrimination for covert markings or labels that is incorporated into, or applied to, most products of commercial interest. The present invention comprises compositions that have been successfully used to invisibly label fabrics, including cotton, wool, and synthetic fibers, and leather goods. These dyes have also been successfully applied to glass and metal surfaces, as well as incorporated into plastics. The invisible labels are not limited to overt application. Rather, the present invention contemplates marking surfaces in a covert manner such that resultant marks, labels, or bar codes are invisible to the naked eye in normal lighting.
Specifically, the compositions are uniquely luminescent at various wavelengths, and allow for a comparison that utilizes the composition""s unique qualities of image, wavelength, and time scale in order to detect the light emitted from the composition. Measurement of the luminescence decay lifetime provides unique xe2x80x9cfingerprintsxe2x80x9d of the luminescent compositions, for purposes of comparative analysis. Luminescence decay lifetimes are variable, and are reproducible and adjustable with the addition of luminescence lifetime modifiers to the compositions, which provide for multivariate lifetime imaging.
In one embodiment of the present invention, luminescence intensities of compositions are recorded as a function of time following initiating pulses of light. Wavelength and time resolution of the luminescence signals produce a unique xe2x80x98fingerprintxe2x80x99 for any composition that is associated with a product or document. This coding of luminescence information can be employed in bars, strips, or layers, and as single features of various shape, or as one and two dimensional arrays. These features can be detected using a scanning device that can store or transmit data for recovery and use in the verification of product or document identity. The compositions display discrete luminescence signals whose decay times are an adjustable variable that depends on the selected metal, the chelating ligand, and modifying agents that provide further control over luminescence lifetime.
In another embodiment of the present invention, these luminescent compositions are doped into materials or on surfaces using solvents as carriers. These compositions can be applied to a variety of materials including paper, card stock, plastic packaging or surfaces, and fabric by brushing, dipping, spraying, aerosol application, writing instruments, or through the use of a conventional inkjet photocopier or devices which employ nozzle feeding mechanisms. Detectable luminescent marks have been demonstrated on materials that include threaded or woven organic materials, credit cards, paper, ink-jet prints, plastic packaging and parts, and metal surfaces. The compositions absorb in the near ultraviolet region (300-400 nm), and are capable of producing readily detected luminescence in the visible (blue, green or red) in relatively narrow bands.
The compositions of the present invention exhibit delayed luminescence, a process of light emission that is normally much less efficient than the commonly observed fluorescence associated with many colored materials. When these two types of emission are time-resolved, normal fluorescent light appears in the time domain of nanoseconds (10xe2x88x929 second), following an initiating light pulse. The processes of long lived luminescence, known as delayed fluorescence or phosphorescence, are active in the time domain of microseconds to seconds (and occasionally longer times). Delayed fluorescence or phosphorescence, on the other hand, occurs on a time scale that is sufficiently slow that detection apparatus based on less sophisticated electronics or on mechanical xe2x80x9cchoppingxe2x80x9d will suffice.
In an embodiment of the present invention, the reading of specific wavelengths of emitted light, or the comparison of luminescent images through the use of any number of light photodetectors, including spectrometers, florimeters, and phosphorimeters is contemplated.
The luminescent signals, referred to as xe2x80x9cfingerprintsxe2x80x9d, are unique to a given composition and the substrate to which it is applied. While it is not intended that the present invention be limited to any specific device by which delayed luminescence can be compared, in one embodiment of the present invention, the detection and comparison of wavelengths would be achieved using a variety of commercially available instruments. For example, the detection of luminescent radiation, in the recording of steady state emission and excitation spectra, can be carried out using a Photon Technology International, Inc., QuantaMaster luminescence spectrometer, model SE-900M. Emission lifetimes can be measured using a PTI TimeMaster fluorescence lifetime spectrometer, equipped with a GL-3300 nitrogen/dye laser as the excitation source (e.g. xcexexc=337 nm), a DG-535 delay/pulse generator and a strobe detector. Similar instruments, also capable of measuring luminescence decay times in the range from 100 ps to seconds are also available from other vendors (e.g. Edinburgh Analytical Instruments FS900 spectroflourimeter system). These commercial instruments can be configured to record luminescence spectra and luminescence excitation spectra for the entire range of ultraviolet, visible and infrared wavelengths (e.g. 200-900 nm). Software available from the fluorimeter vendors is capable of decay time analysis including, for example, the computation of luminescence lifetimes, the determination of multiple exponential decay functions, and a statistical analysis of goodness-of-fit to the decay data.
In another embodiment, the comparison of luminescence may be carried out using devices of simple design that allow portability and ease of operation by personnel having minimal training in the field of luminescence spectroscopy. For example, a compact hand-held apparatus can be fabricated that incorporates a readily available emitting diode light source, and inexpensive diode detector, and simple circuity that can be understood and implemented by persons skilled in the art of detector electronics. Such a device is illustrated in the description of a UV-scanning apparatus, constructed from available optical and electronic components, that has the capability of discriminating slow-decaying luminescence. These components include a very low-leakage Hamamatsu photodiode (R2506-02), a high impedance (10-12 ohm) FET operational amplifier (TLO 64), CMOS analog switches (74HC 4066), and a MOSFET low on resistance transistor (IRF 7503) for UV modulation. Utilizing a double differential scheme, the apparatus is relatively insensitive to ambient light and/or temperature changes. Extremely weak signals of luminescence can be sensed by the low-leakage photodiode, if signals are amplified and averaged over multiple periods of the clock generator (LM311) to improve the signal/noise ratio.
In another embodiment of the present invention, the coding of luminescence information is detected using a scanning device that can store or transmit data for recovery and use in the verification of product or document identity. The storage and transmission of data for recovery may be accomplished via any type of cable or wire, and is not limited to any particular distances. Rather, the present invention may be used to achieve the storage and transmission of data for recovery from one physical point to one or several other specified locations.
In another embodiment of the invention, chelate-luminescence lifetime modifier compositions offer unique combinations of luminescence, durability, long shelf life, and a high level of difficulty with regard to counterfeit reproduction.
In a further embodiment of the present invention, the marking system can be rotated, or xe2x80x9cturned overxe2x80x9d on a timely basis through a systematic tuning of the luminescent tags such that the delay-time intervals for comparison are variable, as well as the wavelengths of emitted light.
In another embodiment of the present invention, the specific wavelength signals of emitted light can be read using photodetectors, and then transmitted via cable or telephone wires, and stored or compared at a distal site.
In another embodiment of the present invention, novel chelate/substrate combinations are contemplated. Such combinations comprise the use of any substrate, such as paper (e.g. plain, colored, currency, checks, stocks, bonds), cloth, plastic, leather, thread, metal, glass, or other convenient form, used in conjunction with a metal from the lanthanide series of chemical elements. The present invention does not limit the metal to the lanthanide series of chemical elements. A variety of metal elements are contemplated, and the compositions of the present invention. may comprise any type of metal elements.